Arm numbness

I am a 20 year old female and in pretty good shape.  I've been noticing numbness in my hands when I wake up after a night of sleep. I've never had this problem before and I first thought that it maybe was how I was sleeping but the problems have persisted.  My left arm has been increasingly been getting numb as I sleep.  It started out as just my hand but now the numbess goes all the way up to my elbow.  I donated blood from my left arm last week and that is when the numbness started not being in just my hand.  I've always had very cold hands and I'm not sure if that is related to this new numbness.  Also my grandmother has a heart bivalve(?) so there is a chance that I could have that condition as well but I've never been checked.